Such valves comprise two carrier elements mounted to move in rotation relative to each other, e.g. the valve body and the shaft of the flow regulating butterfly (or the valve control shaft), together with a magnetic angular-position sensor mounted between the carrier elements. The sensor comprises firstly a magnetic member defining a working zone in which there extends a magnetic field having field lines perpendicular to the axis of rotation, and secondly a detector member having at least one magneto-sensitive probe extending in the working zone in a plane perpendicular to the plane of the field lines in order to provide an electric signal that is function of the angular orientation of the probe relative to the field lines that it intersects.
In general, it is desired to obtain sensors that deliver a linear signal. However this requirement for linearity means that the magnetic member must be given a structure that is complex, such that the resulting signal is very sensitive to the probe being offset relative to its nominal position in the working zone.